Computer Science Fundamentals: From Assembly to Operating Systems

Posted on Jan 13, 2025 in Computers

Second-Generation: Assembly Language

  • A mnemonic system for representing machine instructions:
    • Mnemonic names for op-codes
    • Identifiers: Descriptive names for memory locations, chosen by the programmer

Assembly Language Characteristics

  • One-to-one correspondence between machine instructions and assembly instructions:
    • The programmer must think like the machine
  • Inherently machine-dependent
  • Converted to machine language by a program called an assembler

Third-Generation Languages

  • Uses high-level primitives:
    • Similar to our pseudocode in Chapter 5
  • Machine independent (mostly)
  • Examples: FORTRAN, COBOL
  • Each primitive corresponds to a sequence of machine language instructions
  • Converted to machine language by a program called a compiler

Procedural Units

  • Local versus Global Variables
  • Formal versus Actual Parameters
  • Passing parameters by value versus reference
  • Procedures versus Functions

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Protocols

  • CSMA/CD:
    • Used in Ethernet
    • Silent bus provides the right to introduce a new message
  • CSMA/CA:
    • Used in WiFi
    • Hidden terminal problem

Inter-process Communication

Client-Server

One server, many clients. The server must execute continuously. The client initiates communication.

Peer-to-Peer (P2P)

Two processes communicating as equals. Peer processes can be short-lived.

Traditional Internet Applications

  • Electronic Mail (email):
    • Domain mail server collects incoming mail and transmits outgoing mail
    • Mail server delivers collected incoming mail to clients via POP3 or IMAP
  • File Transfer Protocol (FTP)
  • Telnet and SSH

World Wide Web

  • Hypertext and HTTP
  • Browser gets documents from the Web server
  • Documents identified by URLs

Hypertext Document Format

  • Encoded as a text file
  • Contains tags to communicate with the browser:
    • Appearance
    • <h1> to start a level one heading
    • <p> to start a new paragraph
    • Links to other documents and content
    • Insert images: <img src="" alt="">

Client-Side Versus Server-Side

  • Client-side activities:
    • Examples: Java applets, JavaScript, Macromedia Flash
  • Server-side activities:
    • Common Gateway Interface (CGI)
    • Servlets
    • PHP

Internet Software Layers

  • Application: Constructs the message with the address
  • Transport: Chops the message into packets
  • Network: Handles routing through the Internet
  • Link: Handles the actual transmission of packets

TCP/IP Protocol Suite

  • Transport Layer:
    • TCP
    • UDP (User Datagram Protocol)
  • Network Layer:
    • IP (IPv4 and IPv6)

Functions of Operating Systems

  • Oversee the operation of the computer
  • Store and retrieve files
  • Schedule programs for execution
  • Coordinate the execution of programs

Evolution of Shared Computing

  • Batch processing
  • Interactive processing:
    • Requires real-time processing
  • Time-sharing/Multitasking:
    • Implemented by Multiprogramming
  • Multiprocessor machines

Types of Software

  • Application software:
    • Performs specific tasks for users
  • System software:
    • Provides infrastructure for application software
    • Consists of the operating system and utility software

Operating System Components

  • User Interface: Communicates with users:
    • Text-based (Shell)
    • Graphical User Interface (GUI)
  • Kernel: Performs basic required functions:
    • File manager
    • Device drivers
    • Memory manager
    • Scheduler and dispatcher

File Manager

  • Directory (or Folder): A user-created bundle of files and other directories (subdirectories)
  • Directory Path: A sequence of directories within directories

Memory Manager

  • Allocates space in main memory
  • May create the illusion that the machine has more memory than it actually does (virtual memory) by playing a “shell game” in which blocks of data (pages) are shifted back and forth between main memory and mass storage

Getting it Started (Bootstrapping)

  • Boot loader: Program in ROM (example of firmware):
    • Run by the CPU when power is turned on
    • Transfers the operating system from mass storage to main memory
    • Executes a jump to the operating system

Processes

  • Process: The activity of executing a program
  • Process State: Current status of the activity:
    • Program counter
    • General purpose registers
    • Related portion of main memory

Process Administration

  • Scheduler: Adds new processes to the process table and removes completed processes from the process table
  • Dispatcher: Controls the allocation of time slices to the processes in the process table. The end of a time slice is signaled by an interrupt.

Representing Numeric Values

  • Binary notation: Uses bits to represent a number in base two
  • Limitations of computer representations of numeric values:
    • Overflow: Occurs when a value is too big to be represented
    • Truncation: Occurs when a value cannot be represented accurately

Representing Images

  • Bit map techniques:
    • Pixel: Short for “picture element”
    • RGB
    • Luminance and chrominance
  • Vector techniques:
    • Scalable
    • TrueType and PostScript

Representing Sound

  • Sampling techniques:
    • Used for high-quality recordings
    • Records actual audio
  • MIDI:
    • Used in music synthesizers
    • Records “musical score”

Compressing Audio and Video

  • MPEG:
    • High-definition television broadcast
    • Video conferencing
  • MP3:
    • Temporal masking
    • Frequency masking

Communication Errors

  • Parity bits (even versus odd)
  • Checkbytes
  • Error-correcting codes